Video games such as action games and role-playing games make characters act in a three-dimensional virtual game space corresponding to operation input by users. Various three-dimensional objects are located in the three-dimensional virtual game space and they are generated by computer graphics. An image which a virtual camera in the virtual space shoots is displayed on a game screen and a user operates a player character while watching the game screen.
In the game which has the three-dimensional virtual game space, a light from a light source located in a predetermined position in the virtual space affects a three-dimensional object located in the three-dimensional space, and then it is possible to show a realistic three-dimensional space. Particularly, when a light-transmitting three-dimensional object is located between the virtual camera and the light source, or when a transmitted light is located, a technique for showing transmission of the light on the light-transmitting object (for example volumetric lighting) is known (for example Non-patent literature 1 and 2).    Non-patent literature 1: Naty Hoffman, Arcot J Preetham, “Rendering Outdoor Light Scattering in Real Time”, Game Developers Conference 2002, (ATI Technologies Inc.), [online] Jan. 13, 2016, <http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/ATI-LightScattering.pdf>    Non-patent literature 2: Balazs Toth, Tamas Umenhoffer, “Real-Time Volumetric Lighting in Participating Media”, Eurographics 2009, [online] Jan. 13, 2016, <http://sirkan.iit.bme.hu/˜szirmay/lightshaft.pdf>